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Sounds like you may have a leak in the intake system. Check for hoses that me not be completely on connectors, tears in any of the pipes etc..

Could be something's up with your boost controller.
I had a similar problem in that my car dropped its maximum boost from 14lbs down to 8 lbs for no apparent reason.

Played around with the boost controller and the boost came back.

Check the connections, both electrical and physical, and see if something's not quite right.

Rattling sounds like a bit of the compressor wheel is now in your exhaust? I certainly hope not.

Do you have a WBO2 gauge? If so, what is the AFR doing under full boost? I assume the you have a MAP sensor for the wolf rather than using the original AFM? Where is the MAP sensor getting its readings from i.e. before or after intercooler?
It could be that the wastegate is either opening early, or not closing properly thereby leaking boost.

Good luck.

J.

i had similar symptoms when i had a boost leak.

my avo intercooler had a threaded hole on one of the end tanks, for a bolt that held the intercooler onto a bracket. anyway the bolt came out thus boost was leaking out. a loose bracket could also cause a rattling noise too, i suppose. probably a long shot but maybe your intercooler or pipework has some brackets somewhere that may have come loose, or a loose hose clamp etc..

oh yeh, i didn't have an ebc tho.

^^^^ What Fatty said.

I had a the odd pipe clamp come loose,the pipe would slip off and I would leak boost, but usually I would suffer total boot loss, not partial.

Are you using a blow off valve.....it may not be sealing properly or the wastgate actuator diaphragm could be gone/going and allowing the wastegate to open early.

I have read on either the big forum or on the Miata Turbo forum that someone had problems with a wastegate not closing fully due to the plate being damaged or out of specification....but I think this was a problem that began as soon as the turbo had been installed....not later down the line.


J

Back in the day, wastegate's were known to break if they were slammed open and shut too harshly. Could be a possibility if you've been hitting the rev limiter... A broken wastegate flap would then leak exhaust gas past the exhaust wheel, resulting in lower peak boost pressures.

Take out your spark plugs,see if one of them is fouling up more than the others,gap the plugs to .8mm,it could be one of the injectors sticking, so they may need a clean.

Sasso,
Sounds like you have a coil pack on the way out, Scooter did it to me and sh*t I had some fun checking it out(diesel mechanics hate petrol motors),does it seem to be worse after a good run and then let the car cool down?? Pull out the multi meter and test H and L voltage sides.

Terry